This project involves utilization of single neuron recording techniques in behaving monkeys to study brain mechansms underlying volitional motor performance. It has been shown that the laws of reflex action known to operate at the level of the spinal cord also operate at the level of the cerebral cortex. Motor cortex pyramidal tract neurons (PTNs) are impaired upon by afferent inputs which constitute the incoming limb of a transcortical loop. Thus, the phylogenetically new pyramidal tract system of the mammal is subject to the same laws of reflex action that characterize the phylogenetically older components of motor control systems. In addition to being driven by a servo system which stabilized movement and posture, PTNs are driven by a second major set of inputs, and it is this second set of inputs that underlies internally generated motor programs. These programs, reaching the motor cortex from the thalamus, are themselves a poduct of activity in basal ganglia and cerebellum.